Rice produces fluorinated nanodiamonds, graphene, and concentric carbon through flash Joule heating
Picture: Rice University chemist's mechanism on the evolution of fluorinated flash nanocarbon phases shows longer and larger stages of energy input. Carbon and fluorine atoms first form a diamond lattice, then graphene, and finally polyhedral concentric carbon. see more
Image source: Weiyin Chen/Illustration by Rice University
Houston-(June 21, 2021)-Diamonds may be just one aspect of exposure to a flash of heat, but this makes it easier to obtain.
Rice University chemist James Tour’s laboratory is now able to "evolve" carbon through phases including valuable nanodiamonds by strictly controlling the flash Joule heating process they developed 18 months ago.
Most importantly, they can stop the process at will to get the product they want.
In the American Chemical Society journal ACS Nano, researchers led by Tour and graduate student and lead author Weiyin Chen showed that the addition of organic fluorine compounds and fluoride precursors to elemental carbon black makes it difficult to flash. The allotropes obtained include fluoride nanodiamonds, fluorinated chaotic layer graphene, and fluorinated concentric carbon.
With the flash process launched in 2020, strong electric shocks can convert almost any source of carbon into the original vortex graphene layer in less than a second. ("Turbostratic" means that there is no strong bond between the layers, making them easier to separate in solution.)
The new work shows that the product can be modified or functionalized at the same time. The duration of the flash is between 10 and 500 milliseconds, which determines the final carbon allotrope.
The difficulty lies in how to preserve fluorine atoms, because ultra-high temperature will cause all atoms except carbon to volatilize. To overcome this problem, the team used a Teflon tube sealed with graphite gaskets and high-melting tungsten rods to keep the reactants inside and avoid the loss of fluorine atoms at ultra-high temperatures. Tour said that the improved sealing tube is very important.
"In industry, small diamonds have long been used in cutting tools and electrical insulators," he said. "The fluorinated version here provides a way to modify these structures. The demand for graphene is great, and the fluorinated family is newly produced here in bulk."
Nanodiamonds are microscopic crystals—or crystal regions—showing the same lattice of carbon atoms as macroscopic diamonds. When they were first discovered in the 1960s, they were made under the high temperatures and pressures of explosions.
In recent years, researchers have discovered that chemical processes can produce the same crystal lattice. Rice theorist Boris Yakobson (Boris Yakobson) a report last year showed how fluorine can help make nanodiamonds without high pressure. Tour’s own laboratory demonstrated the use of pulsed lasers to transform Teflon Converted into fluorinated nano-diamond.
Nanodiamonds are very suitable for electronic applications because they can be doped to be used as wide band gap semiconductors, which is an important part of Rice and Army Research Laboratories' current research.
The new process simplifies the doped part, not only for nanodiamonds, but also for other allotropes. Tour said that Rice Labs is also exploring the use of boron, phosphorus and nitrogen as additives.
With a longer flash time, the researchers embedded nanodiamonds in a concentric shell of carbon fluoride. A longer exposure time will completely turn the diamond into a shell from the outside to the inside.
"The concentric shell structure has been used as a lubricant additive, and this flash method may provide a cheap and fast route to these formations," Tour said.
The co-authors of the paper are Rice University graduate students Li Tianci, Wang Zhe, Wala Algozeeb, Emily McHugh, Kevin Wyss, Paul Advincula, Jacob Beckham and Bo Jiang, research scientist Carter Kittrell, and alumni Duy Xuan Luong and Michael Stanford. Tour is the chair of the chemistry department of TT and WF Chao, and a professor of computer science, materials science and nanoengineering at Rice University.
The Air Force Office of Scientific Research and the Department of Energy supported this research.
Read the abstract at https://pubs.acs.org/doi/10.1021/acsnano.1c03536.
This press release can be found online at: https://news.rice.edu/2021/06/21/flashed-nanodiamonds-are-just-a-phase/
Follow Rice news and media relations on Twitter @RiceUNews.
Rice Lab instantly turns garbage into valuable graphene: http://news.rice.edu/2020/01/27/rice-lab-turns-trash-into-valuable-graphene-in-a-flash- 2/
Tour group: https://www.jmtour.com
Department of Chemistry: https://chemistry.rice.edu
West College of Natural Sciences: https://naturalsciences.rice.edu
https://news-network.rice.edu/news/files/2021/06/0621_DIAMOND-1-WEB.jpg
Rice University chemists on the mechanism of the evolution of the fluorinated flash nano-carbon phase showed longer and larger stages of energy input. Carbon and fluorine atoms first form a diamond lattice, then graphene, and finally polyhedral concentric carbon. (Source: Chen Weiyin/Illustrated by Rice University)
https://news-network.rice.edu/news/files/2021/06/0621_DIAMOND-2-WEB.jpg
The transmission electron microscope image shows the nano-diamond lattice. Chemists at Rice University use their flash Joule heating technology to control the phase evolution and doping of carbon. (Source: Tour Group/Rice University)
https://news-network.rice.edu/news/files/2021/06/0621_DIAMOND-3-WEB.jpg
The electron microscope image shows the later stages of the evolution of carbon and fluorine atoms under flash Joule heating. The carbon atoms form a concentric shell around the nanodiamond core. As heating progresses, the diamond phase is replaced by the shell. (Source: Tour Group/Rice University)
Rice University is located on a 300-acre forest campus in Houston and has been ranked as one of the top 20 universities in the United States by U.S. News and World Report. Rice has the highly respected Faculty of Architecture, Business, Continuing Research, Engineering, Humanities, Music, Natural Sciences, and Social Sciences, and is home to the Baker Institute of Public Policy. Rice University has 3,978 undergraduate students and 3,192 graduate students, and the undergraduate to faculty ratio is slightly less than 6 to 1. Its boarding college system has built close communities and life-long friendships, which is one of the reasons why Rice ranked first in terms of race/class interaction and quality of life in the Princeton Review. Rice was also named the best value among private universities by Kiplinger's personal finance.
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Copyright © 2021 American Association for the Advancement of Science (AAAS)